1. Field of the Invention
The present invention relates to a logarithmic function generating system wherein the time constant of a time constant circuit is increased successively and a logarithmic function with a time as a variable is generated by approximating it with a broken line.
2. Description of the Prior Art
The logarithmic function generators heretofore known in the art include for example analog type logarithmic function generators wherein the fact that the voltage-current characteristic of diodes is a logarithmic characteristic is utilized to generate an output voltage bearing a logarithmic relation to the input voltage and digital type logarithmic function generators wherein a logarithmic function is generated in an approximate manner in accordance with series expansion formulas of the logarithmic function. In the case of the former analog type generators, due to nonuniformity in the characteristics of diodes of the same type, it has been difficult to obtain logarithmic function generators having the uniform characteristics. There has been another disadvantage that the characteristics of diodes are liable to change with temperature changes and hence the resulting logarithmic function voltage is unstable.
In the case of the digital type generators, it has been necessary to use a complicated computing circuit for realizing the required series expansion formulas. There has been another disadvantage that the circuit construction tends to become extremely large and complicated in order to ensure a high degree of accuracy.